It depends on how snug they were to begin with and really how thick they started. My last 2 pair went 462 days and 547 days. Since I wasn't jamming them in and out like some here, they were still in good shape. They had compressed to the final stage they were ever going to compress to. But the first season had an extended break-in period which I endured (70 days on that 2nd pair before I decided they weren't going to pack as far as I needed without help) and I wore them around the house before I even skied in them. I did not replace the boots because of the liners, but because of my concern about the life of the shell. The fit was great and I hadn't resorted to thicker insoles or anything.
When I bought new boots this year, I rejected the better-fitting boot because the liner had one section barely better than a freezer bag of thickness and very frankly I want SOME insulation because I prefer cold conditions. I will come to regret that later, I'm sure, as there's more ability to pack out in these and frankly they are far too comfortable for season 1, which I told the guy repeatedly. But realistically at 72 years old, I probably don't need another 10 year boot.
If you've got weird bony protuberances you might have issues. I was blessed with a totally unremarkable foot.
